In intaglio and particularly in rotogravure printing, conventional methods for preparing a new printing surface from a previously etched one normally consists of either stripping, grinding, or replacing entirely the old printing surface.
In the still widely used Ballard process, disclosed in U.S. Pat. No. 1,831,645, a thin copper shell (usually about 0.006 inch thick) is formed over an insulating metal layer and bonded at the ends thereof to an underlying, rotogravure cylinder base. After etching and printing use, the etched shell is stripped off entirely, and a new copper shell is plated on as before to form a new printing surface.
The Ballard process, though convenient and quickly executed, is nevertheless uneconomical since the copper shells once stripped are of no further use and must be disposed of. Further, in plating on the new copper shell, copper anode bars of high purity must be used, and these bars are expensively fabricated. In addition, because each shell is usually plated on to a thickness of 0.006 inch, as compared to a depth of etching generally 0.002 inch deep, a greater possibility of error exists for producing a new rotogravure surface that is not perfectly cylindrical nor longitudinally linear than if a layer of substantially lesser thickness were otherwise to be plated on. Inasmuch as rotogravure speeds currently approach 1800-5000 ft./min., the rotogravure cylinder must be near perfectly true, or inaccuracies as small as 0.002 inch will cause wrinkling of and unevenness of tone in the printed matter.
An alternative method consists of grinding down the old printing surface below the level of the etching, and then replating metal to the desired thickness. Not only is this method time consuming, but also the resultant surface is far from smooth and often scored by particles loosened during grinding. Most importantly, this method using conventional equipment does not attain the high degree of cylndrical and linear trueness required for high speed rotogravure printing.
Another method for preparing an intaglio surface, disclosed in U.S. Pat. No. 2,373,087 to Alger, consists of etching a screen pattern onto the copper surface, filling the recesses of the screen pattern with insulative material, plating the grid lines of the screen pattern with chromium, removing the insulative material, and replating the recesses full with copper, which will adhere to the copper in the recesses but not to the chromium on the grid lines. Thereafter, an etched surface previously prepared in this manner can be reused for another impression simply by replating after use directly into the etched recesses.
It has been found, however, that the Alger method results in the etched recesses being replated to uneven heights, thereby requiring further grinding and polishing. In addition, use of a pre-formed chrome grid pattern precludes a printing surface prepared as above from being etched by the pecking stylus of heliokleishographic machines which are currently being introduced to and widely adopted in rotogravure.